Electrically conductive polymeric compositions



United States PatentOfitice 3,73,784 Patented Jan. 15, 1963 3,073,784ELECTRICALLY CONDUCTIVE POLYMERIC COMPOSITIONS Andrew Laszlo Endrey,Fairport Harbor, Ohio, assignor to E. I. du Pont de Nemours and Company,Wilmington, Del., a corporation of Delaware No Drawing. Filed July 2,1959, Ser. No. 824,461 10 Claims. ((31. 252-518) This invention relatesto the preparation of shapeable polymeric compositions, polyimidestructures containing particles and to a novel process for theproduction thereof.

Polyimide structures, particularly structures of thepolypyromellitimides, are useful and resistant to degradation at hightemperature. As a vehicle for metals or metal salts in the preparationof electrically conductive tapes, luminescent tiles, photosensitivematerials and decorative films, fibers and the like, the polyimideswould seem to be ideal. However, the same outstanding physical andchemical properties that would make these metal or salt-containingpolymers extremely useful in the form of shaped structures such asfilms, filaments, tubing, etc., make it extremely diflicult to shape thepolymers into useful structures by the ordinary methods of extrusion orinjection molding.

The object of the present invention is a process for formingsilver-containing polyimide shaped structures. Another object is to formsuch structures containing silver particles of less than 1 micron. Otherobjects will appear hereinafter.

The objects are accomplished by first forming a composition containingat least one polyamide-acid having an inherent viscosity of at least0.1, preferably 0.3- .0; then reacting the polyamide-acid compositionwith a silver salt of an oxy acid of carbon to form the silver salt ofthe polyamide-acid; then shaping the silver salt of the polyamide-acidinto a structure; and, thereafter, converting the structure to apolyimide structure containing particles of silver.

The process may be divided into four steps:

(1) Forming the polyamide-acid composition.

(2) Converting the polyamide-acid into its salt.

(3) Shaping the polyamide-acid salt into a useful structure.

(4) Converting the polyamide-acid salt to a metalcontaining polyimide.

Each of these steps will be discussed separately in subsequent portionsof this specification.

FORMING POLYAMlDE-ACID COMPOSITIONS The process for preparing thepolyamide-acid composition involves reacting at least one organicdiamine having the structural formula:

H N-R'NH wherein R is a divalent radical containing at least 2 carbonatoms, the two amino groups of said diamine each attached to separatecarbon atoms of said divalent radical; with at least one tetracarboxylicacid dianhydride having the structural formula:

II II o o wherein R is a tetravalent radical containing at least 2carbon atoms, no more than 2 carbonyl groups of said dianhydrideattached to any one carbon atom of said tetravalent radical; in anorganic polar solvent under anhydrous conditions while maintaining thetemperature throughout the reaction below 60 0., preferably below 50 C.

It should be understood that it is not necessary that the polymericcomponent of the composition be composed entirely of the polyamide-acid.This is particularly true when conversion to the polyimide iscontemplated subsequent to shaping the polyamide-acid salt. To retainits shapeability as the salt, the polymeric component of the compositionshould contain at least 50% of the polyamide-acid; the remainder may bethe more diificult to mold conversion product. Thus, while theaforementioned process for preparing the polyamide-acid should beconducted below 50 C. to provide substantially of the polyamide-acid,temperatures up to 60 C. will still provide a composition containing atleast 50% of the polyamide-acid in the polymeric component and, in thecase of some polyamide-acids, will provide 100% of the polyamide-acid.It is also within the scope of the present invention to convert aportion of the polyamide-acid to the polyimide by heat, treatment withan acetic anhydridepyridine mixture or treatment with a carbodiimide,e.g.,-

dicyclohexylcarbodiimide. However, the polymeric com ponent of thecomposition at the end of this step should contain at least 50% of theunconverted polyamide-acid. It should be understood that after thepolyamide-acid has been formed, it may be necessary to warm thecomposition in order to insure substantially complete dissolution of thepolyamide-acid in the solvent.

The preferred process involves premixing equimolar amounts of thediamine and the dianhydride as dry solids and then adding the mixture,in small proportions and with agitation, to the organic polar solvent.Premixing the ingredients and then adding them in small proportions tothe solvent provides relatively simple means for controlling thetemperature and the rateof the process. Since the reaction is exothermicand tends to accelerate very rapidly, it is important to regulate theadditions to maintain the reaction temperature below 60 C. However, theorder of addition may be varied within the scope of the presentinvention. After premixing the diamine and the dianhydride, the solventmay be added to the mixture with agitation. It is also possible todissolve the diamine in the organic polar solvent while agitating and toadd the dianhydride slowly to control the reaction temperature.Ordinarily, in this latter process the last portion of the dianhydrideis added with part of the organic polar solvent. Another possible methodinvolves adding the reactants to the solvent in small proportions, notas a premixture, but alternately; first diamine, then dianhydride, thendiamine, etc. In any event, it is advisable to agitate the solutionpolymerization system after the additions are completed until maximumviscosity denoting maximum polymerization is obtained.

The degree of polymerization of the polyamide-acid is subject todeliberate control. The use of equal molar amounts of the reactantsunder the prescribed conditions provides polyamide-acids of very highmolecular weight. The use of either reactant in large excess limits theextent of polymerization. However, up to 5% excess of either the diamineor the dianhydride may be used in the process. More than 5% excess ofeither reactant results in an undesirably low molecular weightpolyamide-acid. It is desirable to use l-3% excess of either reactant,preferably the dianhydride, to control the molecular weight of thepolyamide-acid. Besides using an excess of one reactant to limit themolecular weight of the polyamide-acid, a chain terminating agent suchas phthalic anhydride may be used to cap the ends of the polymer chains.

In the preparation of the polyamide-acid compositions, it is essentialthat the molecular weight be such that the inherent viscosity of thepolymer is at least 0.1, preferably 0.3-5.0. The inherent viscosity ismeasured at .30"

C. at a concentration of 0.5% by weight of the polymer in a suitablesolvent. The viscosity of the polymer solution is measured relative tothat of the solvent alone and the inherent viscosity of slutio nviscosity of solvent 0 where C is the concentration expressed in gramsof polymer per 100 milliliters of solution. polymer art, inherentviscosity is directly related to the molecular weight of the polymer.

The quantity of organic polar solvent used in preparing thepolyarnide-acid composition need only be sufficient to dissolve thediamine and to provide, with the ultimate polymeric salt componentdissolved therein, a sufiiciently low viscosity for forming thecomposition into shaped articles. It has been found that the mostsuccessful results are obtained when the solvent represents at least 85%of both the polyamide-acid solution and final polymeric salt solution.That is, the solution should contain 0.05- 15%, preferably -10% of thepolymeric component.

The starting materials for forming the polyamide-acid composition areorganic diamines and tetracanboxylic acid dianhydrides. The organicdiamines are characterized by the formula: H N-R'NH wherein R, thedivalent radical, may be selected from the following groups: aromatic,aliphatic, cycloaliphatic, combination of aromatic and aliphatic, andsubstituted groups thereof. The most useful diamines are the primarydiamines. However, secondary diamines such as piperazine may be used toproduce polyamide-acid salt compositions where conversion into thepolyimide is not contemplated. The preferred R groups in the diaminesare those containing at least 6 carbon atoms characterized by benzenoidunsaturation. Among the diamines which are suitable for use in thepresent invention are:

meta-phenylene diamine, para-phenylene diamine; 4,4-diamino-diphenylpropane; 4,4'-diamine-diphenyl methane; benzidine; 4,4'-diamino-diphenylsulfide; 4,4'-diamino-diphenyl sulfone; 3,3'-diamino-diphenyl sulfone;4,4'-diamino-diphenyl ether; 1,5-diamino-naphthalene,3,3'-dimethyl-4,4'-biphenyl diamine; 3,3'-dimethoxy benzidine;2,4-bis(beta-amino-t-butyl)toluene;bis-(para-beta-amino-t-butyl-phenyl)ether; bis-(parabeta-methyldelta-amino-pentyl)benzene;bis-para-(l,1-dimethyl-5-amino-pentyl)benzene;l-isopropyl-Z,4-metaphenylene diamine; m-xylylene diamine; 6-xylylenediamine; di(para-amino-cyclohexyl)methane; hexamethylene diamine;heptamethylene diamine; octamethylene diamine; nonamethylene diamine;decamethylene diamine; diamino-propyl tetramethylene diamine;3-methylheptamethylene diamine; 4,4-dimethylheptamethylene diamine;2,11-diamino-dodecane; 1,2-bis-(3-amino-propoxy ethane); 2,2-dimethylpropylene diamine; 3-methoxy-hexamethylene diamine;2,5-dimethylhexamethylene diamine; 2,5-dimethylheptamethylene diamine;3-methylheptamethylene diamine; S-methyl-nonamethylene diamine;2,17-diamin0-eicosadecane; 1,4-diamino-cyclohexane;1,10-diamino-1,IO-dimethyl decane;

natural logarithm viscosity:

As known in the v 1,IZ-diamino-octadecane; 2 2)3 2)2 2)3 2; 2 2)3 2)3 2E 2)3 I3) 2)3 2; piperazme;

and mixtures thereof. Particularly desirable mixtures include:4,4'-diamino-diphenyl methane and para-phenylene diamine;4,4-diamino-diphenyl propane and metaphenylene diamine; and4,4'-diamino-diphenyl propane and benzidine; benzidine andmeta-phenylene diamine; meta-phenylene diamine, para-phenylene diamineand benzidine; meta-phenylene diamine and para-phenylcne diamine;4,4-diamino-diphenyl ether and benzidine; 4,4- diamino-diphenyl sulfideand benzidine; and 4,4-diaminodiphenyl sulfide and 4,4-diamino-diphenylether.

The tetracarboxylic acid dianhydrides are characterized by the followingformula:

wherein R is a tetravalent radical selected from the group consisting ofaromatic, aliphatic, cycloaliphatic, combination of aromatic andaliphatic, and substituted groups thereof. However, the preferreddianhydrides are those in which the R groups have at least 6 carbonatoms characterized -by benzenoid unsaturation, wherein the 4 carbonylgroups of the dianhydride are each attached to separate carbon atoms andwherein each pair of carbonyl groups is directly attached to adjacentcarbon atoms in the R group to provide a 5-membered ring as follows:

li o-t Illustrations of dianhydrides suitable for use in the presentinvention include: pyromellitic dianhydride, 2,3,6,7- naphthalenetetracarboxylic dianhydride, 3,3,4,4'-diphenyl tetracarboxylicdianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride,2,2,3,3'-diphenyl tetracarboxylic dianhydride,2,2-bis(3,4-dicarboxyphenyl) pro pane dianhydride, 3,4-dicarboxyphenylsulfone dianhydride, perylene 3,4,9,10-tetracarboxylic acid dianhydride,bis(3,4-dicarboxyphenyl) ether dianhydride, etc.

The solvents useful in the solution polymerization process forsynthesizing the polyamide-acid compositions are the organic polarsolvents having a dipole moment whose functional groups do not reactwith the diamines or the dianhydrides. Besides being inert to the systemand being a solvent for the product, the organic polar solvent must be asolvent for at least one of the reactants, preferably for both of thereactants. The normally liquid organic polar solvents of theN,N-dialkylcarboxylamide class are useful as solvents in the process ofthis invention. The preferred solvents are the lower molecular weightmembers of this class, particularly N,N-dimethylformamide andN,N-dimethylacetamide. They may easily be removed from thepolyamide-acid salts and/or the shaped articles of the polyamide-acidsalts by evaporation, displacement or diffusion. Other typical compoundsof this useful class of solvents are: N,N-diethylformamide,N,N-diethylacetamide, N,N-dimethylmethoxy acetamide, etc. Other organicpolar solvents which may be used in the present invention are:dirnethylsulfoxide, dicthylsulfoxide, N-methyl-Z-pyrrolidone, pyridine,dimethylsulfone, diethylsulfone, dipropylsulfone,hexamethylphosphoramide, tetramethylene sulfone, dimethyltetramethylenesulfone, dimethoxytetrarnethylene sulfone. The solvents can be usedalone, in combinations of solvents, or in combinations with nonsolventssuch as benzene, benzonitrile, dioxane, butyrolactone, xylene, tolueneand cyclohexane. However, the addition of water cannot be tolerated. Itis necessary that the process be conducted in an essentially anhydrouscondition.

CONVERTING INTO POLYAMIDE-ACID SALT AND SHAPING THE SALT The conversionof the polyamide-acid, which comprises at least 50% of the polymericcomponent of the composition produced in the first step, is accomplished-by adding a solution in an organic polar solvent of a silver salt of anoxy acid of carbon. The metathetical reaction is permitted to take placewhile maintaining the temperature within a range of 050 C. The silversalts are those having as their negative ion, ions derived frommonocarboxylic or polycarboxylic acids such as a fatty acid (e.g.,formic, acetic or propionic acid), a dicarboxylic aliphatic acid (e.g.,oxalic or succinic acid), an unsaturated acid (e.g., maleic or furnaricacid), and ether acid (e.g.,- diglycolic or dilactic acid), a hydroxyacid -(e.g., tartaric or citric acid) or an aromatic acid (e.g., benzoicor phthalic acid), or the ion derived from carbonic acid.

It should be understood that when it is desired to.use thepolyamide-acid compositions as such' as a coating or an impregnant,i.e., without converting to the polyimide plus the free metal, thenother group I 1 metals such as sodium, lithium or potassium as well assilver may be used. However, because of their reactivity, sodium,lithium and potassium are not very useful as free metal parti-' cles inany ultimate polyimide structure.

The metal salt is preferably added as part of a solution in an organicsolvent. The organic solvent is preferably the same as that usedpreviously in the preparation of the polyamide-acid but may be any ofthose listed previously, which solvent is a solvent for the particularmetal salt under consideration. If sufficient solvent were used informing the polyamide-acid composition, then the metal salt in solidform may be added in this step.

In the formation of the metal salt of the polyamideacid, rapid stirringand the addition of more solvent or pyridine or a beta-ketonic typecompound such as ethyl acetoacetate are advised to clear any gel orinsoluble matter that may form in the polyamide-acid salt solution. Theviscous salt solution, which should contain preferably at least 85%solvent as discussed previously, is then formed into a useful shapedstructure by molding, casting or extrusion. The viscosity of the saltcomposition for shaping should be sufficiently low for forming thecomposition into shaped articles. The viscosity can be controlled by theaddition of solvent to or removal of it from the viscous dope. Theshaped structure is then dried "by exposure to air at the boilingtemperature of'the solvent for a short period.

The degree of substitution of metal for hydrogen achieved in this stepdepends upon the amount of metal salt added and the temperature and timepermitted for the reaction. In the discussion that follows, asubstitution or 1 mole of metal per polymer unit will be illustrated,i.e., 0.5 mole of metal per carboxyl unit of polyamide-acid. For thepurpose of the present invention, a substitution of 0.1 mole2 moles ofmetal per polymer unit can be used successfully. Thus, the shapeablepolymeric composition at this stage may be described as one comprising0.05- 15% by weight of at least one polyamide-acid salt having therecurring unit:

Tifi t i T wherein denotes isomerism; wherein R is a tetravalent radicalcontaining at least six carbon atoms character- Group I of MendeleefsPeriodic Table of the Elements, Handbook of Chemistry and Physics (25thed.), published'by Chemical Rubber Publishing Co. 4

ized by benzenoid unsaturation, the four carbonyl groups of eachpolyamide-acid unit being attached to separate carbon atoms and eachpair of carbonyl groups being directly attached to adjacent carbon atomsin said tetravalent radical; wherein R is a divalent radical containingat least 2 carbon atoms, the amide groups of adjacent polyamide-acidunits each attached to separate carbon atoms of said divalent radical;and wherein A is selected from the group consisting of hydrogen and aGroup I metal, the minimum substitution of metal per polymer unit being0.1 mole.

dissolved in -99.95% of an organic polar solvent; said polyamide-acidsalt having an inherent viscosity of at least 0.1.

CONVERTING INTO POLYIMIDE The shaped articles composed of at least50%-of'a metal salt of a polyamide-acid may then be converted to therespective polyimide shaped articles. One process involves convertingthe polyamide-acid salts having the recurring units of the followingstructural formula: 1

H000 COOAg R -NC/ o N-R L t I wherein denotes isomerism to polyimidesplus free metal by heating above 50 C. Heating serves to convert pairsof amide and metal-substituted carboxylic acid groups to imide groupsplus free metal particles. Heating may be conducted for a period of afew seconds to several hours. It is preferred to have gradualtemperature increases up to and within the conversion range in order todiscourage the tendency of void and bubble formation within thepolyimides as a result of the water vapor given off and to avoidcrystallization or embrittlement. It has also been found that after thepolyamideacid has been converted to the polyimide in accordance with theabove described heat conversion, if the polyimide is further heated to atemperature of 300500 C. for a short interval (15 seconds to 2 minutes),improvements in the thermal and hydrolytic stabilities of themetalcontaining polyimide structure are obtained.

Other processes for conversion may involve treatment with one or morechemicals which serve to dehydrate the polyamide-acid salt to form thepolyimide plus metal and which also act as effective cyclizing agents.

The presence of polyimides is evidenced by their insolubility in coldbasic reagents as opposed to the rapid solubility of the polyamide-acid.Their presence is also apparent if the polyamide-acid salts are scannedwith infrared during conversion to the polyimide. The spectra initiallyshow a predominating absorption band at ca. 3.1 microns due to the NHbond. This band gradually disappears, and as the reaction progresses,the polyimide absorption band, a doubleton, appears at ca. 5.64 and 5.89microns. When conversion is completed the characteristic polyimide bandpredominates.

It is surprising to note that the final polyimide structures containingsilver particles may be transparent and may not show diffraction by theincorporated particles nor may the particles be visible under anordinary microscope. This means that the particles therein havedimensions smaller than the wave length of light, i.e., the particles donot have dimensions greater than 0.8 micron. In any event, the processof the present invention makes it possible to provide polyimidestructures containing metal particles up to about 1 micron. Any processwhich would attempt to incorporate finely-divided or powderedmetalparticles in a final structure, if such could be accomplished withpolyimide structures, would provide- Example I 4,4-diamino-diphenylmethane, 11.6 grams (0.058 mole) was dissolved in 150 milliliters ofdimethylformamide. To this solution, 12.7 grams (0.058 mole) ofpyromellitic dianhydride was added portionwise with agitation while thesolution was externally cooled with circulating water at approximately15 C. A viscous dope formed which was further diluted with 30milliliters of dimethylformamide to give a solution containing 12% byweight of the polyamide-acid. The inherent viscosity was 2 (0.5%solution in dimethylformamide).

A 10% solution of silver acetate in pyridine, 10.0 grams (0.0058 mole ofsilver) was added with stirring to 20.0 grams of the 12%dimethylformamide solution of the polyamide-acid (0.0058 mole of polymerunit). After a slight initial precipitation, rapid stirring and theaddition of a slight amount of pyridine yielded a clear viscous dope.

A film was cast onto a glass plate with a doctor knife having a 15-milopening. The film was dried at 130 C. for 15 minutes in air in a forceddraft oven. The film was stripped from the glass plate and residualsolvent was removed. The film, which was the silver salt of thepolyamide-acid, was clear, tough and flexible. The film contained 16.4%silver, approximately 0.5 mole per carboxyl unit.

The polyamide-acid salt film was then heated in a vacuum oven under anitrogen atmosphere at a temperature of 300 C. for 30 minutes. A tough,flexible, opaque film with a metallic luster was obtained. This film wasshown to be a polyimide film containing silver particles having theirgreatest dimension of about 0.8 micron by the following tests.

By ordinary chemical analysis, the film was found to contain 21.8%silver as compared to 22.0% calculated on the basis of one atom ofsilver for each polymer unit (for each two imide groups). X-ray analysisshowed strong lines for free metallic silver at 2.36 angstrom units,2.04 angstrom units and 1.23 angstrom units. Strong infrared absorptionwas obtained by conventional techniques at 5.62 microns and 5.80microns, characteristic of the carbonyl groups in polyimides. Thedisappearance of absorption was observed at 3.0 microns, 6.2-6.4 micronsand 3.5-4.5 microns, the first two being characteristic of the amidegroups and the latter being characteristic of the carboxyl groups, bothgroups of the polyamide-acid precursor. At this stage, thesilver-containing polyimide film was not electrically conducting.Further heat treatment of the film for 5-7 hours at 275 C. in airconverted it to an electrically conducting film.

Example 2 A polyamide-acid silver salt film containing 0.75 mole ofsilver per carboxyl unit was prepared as in Example 1 using 7.4 grams ofthe 10% silver acetate solution in pyridine.

The salt was converted to a polyimide film containing silver particlesby heating in air at a temperature of 300 C. for about 3 hours. Theresulting product was electrically conducting.

When heated to 350 C. for minutes, the polyamideacid salt film wasconverted to a polyimide film having metallic surfaces. The productconducted electricity on both surfaces.

Example 3 A dope was prepared from 12.4 grams of metaphenylene diamine,21.1 grams of pyromellitic anhydride,

6.6 grams of acetic anhydride, 13.2 milliliters of pyridine and 99milliliter of dimethylformamide. Analysis showed that approximately 30%of the polyarnide-acid contained in this dope had been converted to thecorresponding polyimide. Ten grams of this dope was reacted with 3.7grams of silver acetate with good stirring. The solution became veryviscous and an additional 5 milliliters of pyridine was added. Theresulting fluid dope was cast at a 10 mil doctor knife opening, dried atC. for 10 minutes to give clear, flexible, silvercontaining films. Thisfilm was heated under vacuum in a nitrogen atmosphere at 300 C. for 30minutes, followed by heating at 380 C. for 30 seconds to relax the film.A very dark, metallic-appearing, flexible, tough film was obtained. Thefilm contained 16.1% of silver, compared with a value of 15.7%calculated for one-half mole of silver for each carboxyl group of thepolyamideacid.

Example 4 A polyamide-acid from 4,4-diamino-diphenylmethane andpyromellitic dianhydride was prepared as described in Example 1.

Fifteen grams of a 10% solution of silver caprylate in pyridine (0.0058mole of silver) was added with stirring to 20.0 grams of the 12%dimethylformamide solution of the polyamide-acid (0.0058 mole of thepolymer unit). This solution was cast into a film, the film was driedand then converted in the silver-containing polyimide film as describedin Example 1. The resulting film that was obtained was similar to thatdescribed in Example 1.

Example 5 4,4'-diamino-diphenyl methane, 10.0 grams was dissolved in 40milliliters of dimethylformamide. To this solution, 11.0 grams ofpyromellitic dianhydride was added portionwise with agitation while thesolution was externally cooled with circulating water at approximately15 C. A viscous dope formed which was further diluted with 60milliliters of dimethylformamide.

Lithium acetate, 5.15 grams, was added with stirring and the solutionwas diluted further with 55 milliliters of dimethylformamide and 25milliliters of glacial acetic acid.

A film was cast onto a glass plate and dried in vacuo at 60 C. for 24hours. The film was stripped from the glass plate and residual solventwas removed. The dry film, which was the lithium salt of thepolyamide-acid, was moderately tough and flexible.

What is claimed is:

1. A shapeable polymeric composition consisting essentially of 0.05-15%by weight of at least one polyamide acid salt having the recurring unit:

groups of adjacent polyamide-acid units each attached to separate carbonatoms of said divalent radical; and wherein A is selected from the groupconsisting of hydrogen and a group I metal, the minimum substitution ofmetal per polymer unit being 0.1 mole,

4. A shapeable polymeric composition as in claim 1- wherein the group 1metal is silver.

5. A shapeable polymeric composition consisting essentially of 0.05-15%by weight of at least one polyamide-- acid salt having the recurringunit:

wherein-e denotes isomerism; wherein R is a tetravalent radicalcontaining at least six carbon atoms characterized by benzenoidunsaturation, the four carbonyl groups of each polyamide-acid unit beingattached to separate carbon atoms and each pair of carbonyl dissolved inat least 85% of an organic polar solvent,-

said solvent being inert to the system and being a solvent for at leastone of the reactants; said polyamide-acid salt having an inherentviscosity of at least 0.1.

6. A process which comprises reacting at least one diamine having thestructural formula:

H N-R'-NH wherein R is a divalent radical containing at least two carbonatoms, with at least one tetracarboxylic acid dianhydride having thestructural formula:

wherein R is a tetravalent radical containing at least six carbon atomscharacterized by benzenoid unsaturation, the four carbonyl groups beingattached to separate carbon atoms and each pair of carbonyl groups beingattached to adjacent carbon atoms in the R radical,

in an organic polar solvent, said solvent being inert to the system andbeing a solvent for at least one of the reactants under substantiallyanhydrous conditions while maintaining the temperature throughout thereaction below C. to form a polymeric composition containing at least50% polyamide-acidhaving the recurring unit as aforesaid; reacting saidpolymeric composition with a silver salt of an oxy acid of carbon, toform a polyamide-acid salt composition containing a minimum of 0.1 molesilver per polymer unit; forming said polyamideacid salt compositioninto a shaped structure; and heating said structure at a temperatureabove 50 C. to convert said polyamide-acid salt structure to apolyamide. structure containing silver particles.

7. A process as in claim 6 wherein the structure is heated further to atemperature of 300 C.500 C. for at least 15 seconds.

8. A process as in claim 6 wherein said diamine is 4,4- diamino diphenylmethane.

9. A process as in claim 6 wherein said dianhydride is pyromelliticdianhydride.

10. A process as in'claim 6 wherein said metal salt is silver acetate.

References Cited in the file of this patent UNITED STATES PATENTS GreatBritain July 25, 1945 UNITED STATES PATENT-OFFICE CERTIFICATE OFCORRECTION Jamaal-3 .15, 1963 Patent No. 3,073,784

Andrew Lasvzlo Endrey r appears in the above numbered pet- It is herebycertified that erro ers Patent should read as ent requiring correctionand that the-said Let'b corrected below Column 10, line 27, for "applyamide". read a polyimide Signed and sealed this, 27th day of August1963.

(SEAL) Attest ERNEST w. SWIDER DAVID Commissioner of Patents AttestingOfficer

6. A PROCESS WHICH COMPRISES REACTING AT LEAST ONE DIAMINE HAVING THESTRUCTURAL FORMULA: H2N-R'' -NH2 WHEREIN R'' IS A DIVALENT RADICALCONTAINING AT LEAST TWO CARBON ATOMS, WITH AT LEAST ONE TETRACARBOXYLICACID DIANHYDRIDE HAVING THE STRUCTURAL FORMULA: